Demonstration of a Methodology to Summarise and Track Air Pollution Effects on Ecosystems at Regional Scales

June 2011


Project funders/partners: SNIFFER, Scottish Environment Protection Agency, Northern Ireland Environment Agency, Environment Agency, Joint Nature Conservation Committee, Scottish Natural Heritage.

Background to research

The existing tools available for investigating impacts of air pollutants on ecosystems consist of national maps and a local level information database in the form of the Air Pollution Information System (APIS, The national maps are based on modelled air pollutant data and underlying habitat maps but cannot readily be interrogated by a user and are not produced on an annual basis. APIS provides what is currently the most comprehensive source of readily available information on the risk associated with air pollution impacts to ecosystems. These two information sources, however, leave a number of key information gaps:

With this in mind, Phase One of this project developed a methodology to summarise the impacts of air pollutants on ecosystems based on critical loads and critical levels, in order to provide an overview of the current risk of harm to ecosystems from air pollutants. The methodology involved a three tier approach, the first two tiers of which were implemented within Phase Two. Tier 1 involved the assessment of habitats data against a combination of critical load and critical level exceedance to determine the overall combined risk (Low, Medium, High) from air pollutants for each 1km x 1km grid square within the UK. Tier 2 enabled a further level of classification within a defined area. The medium and high risk levels were subdivided into four further categories, Level 1 to Level 4, based on the proportion of the given area covered by the worst case risk level. This was further refined during Phase Two to provide ten levels of risk classification, in 10% increments.

Objectives of research

The objective of Phase Two was to demonstrate the value and functionality of the devised methodology and to visualise how the output of the methodology could be presented. Data from a “current” year (2008) was used to demonstrate how current air pollution impacts could be presented at both a UK level and for a defined regional demonstration area: North Yorkshire. Data from three historic years (1998, 2001 and 2005) were used to investigate the sensitivity of the methodology to temporal changes in impacts.

Key findings and recommendations

Both the UK (Tier 1) and regional (Tier 2) maps clearly showed areas of Low, Medium and High risk for individual critical loads and levels. However, the maps showing the overall impacts of all pollutants and habitats were dominated by the High risk category. This was driven by the high amount of deposition of nitrogen on woodland habitats relative to other habitat types. The methodology was shown to be flexible with respect to mapping a combination of habitats and pollutants, to be sensitive to temporal changes in overall impacts and to be applicable to most habitat/pollutant combinations. Specific examples of where such a tool could be useful at a regional level were demonstrated.

There are potentially wide applications of this system using further boundary subsets, for example designated site boundaries, and the Tier 2 classification could provide an important tool for identification and prioritisation of the sites considered to be most at risk. The issues highlighted as requiring further investigation or discussion were as follows:

An investigation of a “dominant habitat methodology” and of an accumulated exceedances methodology was also undertaken. The dominant habitat methodology did not provide any key advantages over the Phase One methodology with respect to a significant reduction in the area dominated by the High risk category. The outputs were also based on a summary of all habitat types, removing the flexibility of allowing the user to select different habitat/pollutant combinations. However this approach could be utilised to identify dominant habitat sites where attention should be focused.

The accumulated exceedances methodology provided the most useful visual outputs showing a large range of impacts. However, this method did not allow for a summary of all impacts from air pollutants to be presented, as per the remit of the tool, as it is based on data for individual pollutants and these cannot simply be added together. An option for potentially utilising the concept of the sum of the proportion of exceedance above a given threshold was suggested and could be further investigated.

The future direction of the methodology depends on two key factors: resources and user requirements. A number of options have been presented as to how this system could be taken forward to the next stage. Each has its challenges with respect to cost and/or functionality. If a compromise is to be made between cost and functionality it is important to fully canvas users to ensure that the functionality of the tool is optimised within the further development of the model.

Key words: air pollution, air quality, classification scheme, critical level, critical load, ecosystem, habitat, pollution, regional scale, risk-based methodology, risk-based approach.

Copies of this report are available from the Foundation, in electronic format on CDRom at £20.00 + VAT or hard copy at £25.00, less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website.